Cattle Grazing Strategies That Limit Stream Bank Degradation
Mike McInnis and Jim McIver
SUMMARY
This report summarizes our two published studies that test whether altering timing
of grazing (McInnis and McIver 2009) or providing cattle with off-stream drinking water
and mineral supplements (McInnis and McIver 2001) can lessen grazing-induced damage
of stream banks. In each 2-year study, grazing treatments were replicated along a
mountain stream in northeastern Oregon. Estimates of stream bank cover and stability
were taken before and after each grazing period. The first study compared early summer
to late summer grazing, and found that cattle spent more time in uplands earlier in the
year when green forage was available, resulting in development of just 3 percent
uncovered stream banks compared to 8 percent late season. Similarly, early summer
grazing resulted in 13 percent unstable stream banks compared to 31 percent later in
summer. Our second study compared stream banks in pastures provided with off-stream
water and mineral supplements to pastures lacking those amenities. Off-stream water and
supplements attracted cattle into the uplands enough to reduce development of ncovered/
unstable stream banks from 9 percent in non-supplemented pastures to just 3 percent in
supplemented pastures.
INTRODUCTION
Riparian areas are critical components of western rangelands and function to store
water, recharge aquifers, moderate flood intensity, maintain water quality by filtering
chemical and organic wastes, trap sediments, and provide habitat for wildlife. Cattle are
naturally attracted to riparian areas because of shade, drinking water, and forage. Roath
and Krueger (1982) estimated 81 percent of forage used by cattle came from a streamside
meadow representing only 2 percent of the grazing area. Such disproportionate use,
especially under conditions of heavy cattle grazing, can lead to a cascading loss of
riparian vegetation, breakdown of stream banks, stream widening, impairment of water
quality, and loss of wildlife habitat. Our studies were part of larger projects that
compared cattle distribution in riparian pastures during early versus late summer (Parsons
et al. 2003) and with versus without off-stream water and mineral supplements (Porath et
al. 2002). Those studies successfully altered distribution of cattle and resulted in
increased use of uplands. The objective of our research was to determine whether such
grazing strategies would limit cattle-induced degradation of stream banks.
METHODS
Research was conducted on the Hall Ranch Unit of Oregon State University’s
Eastern Oregon Agricultural Research Center near Union, Oregon. Nine pastures
(averaging about 28 acres; range 22-37 acres) were delineated along a 1.5-mile reach of
Milk Creek (Fig. 1). Grazing treatments were randomly assigned to pastures within each
of three blocks. Cow-calf pairs were introduced into the grazed pastures to achieve
moderate stocking rates averaging about 1.7 acres/Animal Unit Months (range 1.2-2.2
acres/AUM). Stocking rates and length of grazing bouts were chosen to achieve a
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moderate grazing intensity of about 50 percent utilization of key forage species. Actual
utilization was measured and averaged less than 50 percent in every case.
Figure 1. Schematic diagram (not to scale) showing experimental pastures on Milk Creek
in northeastern Oregon. Each of three blocks contained three grazing treatments (study
no. 1 described in text): (1) nongrazed; (2) early summer grazing (mid-June to mid-July);
(3) late summer grazing (mid-August to mid-September). Black line represents Milk
Creek, which flows from Block 1 in the south through Block 3 in the north. Pasture
arrangement was identical in study no. 2, but grazing treatments differed (see text).
Study No. 1: Altering Timing of Grazing
During 1998 and 1999 three grazing treatments were examined: (1) nongrazed;
(2) early summer grazing (28 days; mid-June to mid-July); and (3) late summer grazing
(28 days; mid-August to mid-September). Estimates of stream bank cover and stability
were taken before and after each grazing period by pacing both sides of the creek and
examining plots (about 20 x 12 inches) along the “greenline” (the first vegetation at the
water’s edge). Additionally, frequency of cattle hoof prints (plots with hoof prints/total
number of plots) was measured as an indicator of cattle presence. Plots were classified as
“covered” if they contained any of the following features: (1) living perennial vegetation
ground cover greater than 50 percent, or (2) roots of deeply-rooted vegetation such as
shrubs or sedges covering more than 50 percent of the plot, or (3) at least 50 percent of
the stream bank surface covered by rocks of cobble size or larger, or (4) at least 50
percent of the bank surface covered by logs 4 inch diameter or larger. Otherwise plots
were rated “uncovered”. Cover estimates were based on visual assessment of the vertical
projection of a polygon drawn around extremities of above-ground parts onto the ground.
Plots were classified “stable” unless they exhibited any of the following features:
(1) blocks of banks broken away and lying in the stream channel adjacent to the bank
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(“bank breakage”), (2) bank sloughed into the stream channel (“slump”), (3) bank
cracked and about to move into stream (“fracture”), (4) bank uncovered as defined above
with an angle visually estimated steeper than 80 degrees from horizontal (“vertical
bank”). Plots exhibiting any of those features were rated “unstable”.
Each plot was rated according to stream bank cover and stability and grouped into
one of four classes: (1) covered/stable, (2) covered/unstable, (3) uncovered/stable, (4)
uncovered/unstable. One person collected all data.
Study No. 2: Providing Off-stream Water and Mineral Supplements
During 1996 and 1997 three replications of each of the following grazing
treatments were studied using the same pasture design described above: (1) nongrazed;
(2) “supplemented” pastures in which free-choice off-stream water and trace mineralized
salt was provided; and (3) “nonsupplemented” pastures in which no off-stream water or
salt was provided. Free-choice off-stream water and salt was provided in supplemented
pastures about 400 yards upslope from Milk Creek. Feeders containing salt were placed
about 15 ft from water troughs. Cow-calf pairs grazed 42 consecutive days beginning
mid-July. Frequency of hoof prints and estimates of stream bank cover and stability were
made before and after grazing the second year of the study using the methods described
above.
RESULTS AND DISCUSSION
Study No. 1: Altering Timing of Grazing
Frequency of plots with cattle hoof prints in nongrazed, early-grazed and lategrazed pastures, respectively, averaged 0 percent, 53 percent (SE+ 11 percent), and 90
percent (SE + 1 percent). Change in stream bank cover resulting from early grazing
(-3 percent) was not statistically different from nongrazed controls, but was significantly
less than the 8 percent reduction in cover observed following late summer grazing (Table
1). Stream bank stability decline resulting from early grazing (-13 percent) was less than
half that observed after late-season grazing (-31 percent). The greatest change was in the
covered/stable category, which declined 10 percent during early summer and 28 percent
during late summer. Grazing resulted in increased percentages of covered/unstable and
uncovered/unstable stream banks, and in each category the increase was greatest for the
late summer grazing treatment. There were proportionally larger changes in stability
compared to cover that resulted from grazing (Table 1). Therefore decline in bank
stability likely contributed more to change in the uncovered/unstable category than did
decreases in cover.
Study #2: Providing Off-Stream Water and Mineral Supplements. Following
grazing, the percentage of plots having cattle hoof prints averaged 0%, 26% (SE + 4) and
31% (SE + 5) in control, supplemented, and non-supplemented pastures, respectively.
While there was a trend for supplemented pastures to have a lower frequency of hoof
prints in the greenline compared to non-supplemented units, the two treatments did not
differ statistically. Neither stream bank cover alone nor stability alone differed between
grazed treatments, and both decreased compared to nongrazed controls (Table 2). When
combined, stream bank cover and stability declined 9% in non-supplemented pastures
compared to only 3% in supplemented pastures. Declines in stream bank stability
contributed more to this change than declines in stream bank cover.
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Table 1. Mean proportions of stream bank (m/100 m of stream bank) before grazing, after
grazing and change for nongrazed pastures (control), early summer grazing (mid-June to midJuly), and late summer grazing (mid-August to mid-September), 1998 and 1999. See McInnis and
McIver (2009) for full data set.
Streambank
parameter
Non-grazed pastures
Early summer grazing
(m/100 m of stream bank)
Before
After
Change
Before
After
Change
Covered
90
91
+1a *
90
87
Stable
92
92
0a
91
83
84
+1a
9
8
7
1
Covered/
stable
Uncovered/
stable
Covered/
unstable
Uncovered/
unstable
Late summer grazing
Before
After
Change
-3a
95
87
-8b
78
-13b
99
68
-31c
81
71
-10b
94
66
-28c
-1a
10
7
-3a
5
2
-3a
7
0a
9
16
+7b
1
21
+20c
1
0a
0
6
+6b
0
11
+11c
___________________________________________________________________________________________________________________________
*
Change within stream bank parameters among treatments (rows) with different superscripts are
significantly different (lsd; P < 0.05; n = 6).
Table 2. Mean proportions of stream bank (m/100 m of stream bank) before grazing (June), after
grazing (September), and change for nongrazed pastures (control), supplemented pastures
(water and mineralized salt), and nonsupplemented pastures, 1997. See McInnis and McIver
(2001) for full data set.
Streambank
parameter
Non-grazed pastures
Supplemented pastures
(m/100 m of stream bank)
Before
After
Change
Before
After
Change
Covered
92
92
0 a*
94
90
Stable
91
91
0a
95
90
90
0a
3
3
5
2
Covered/
stable
Uncovered/
stable
Covered/
unstable
Uncovered/
unstable
Nonsupplemented pastures
Before
After
Change
-4ab
89
83
-6b
85
-10b
93
76
-17b
89
79
-10b
82
68
-14b
0a
5
6
+1a
10
8
-2a
5
0a
5
11
+6ab
8
15
+7b
2
0a
1
4
+3b
0
9
+9c
___________________________________________________________________________________________________________________________
*
Change within stream bank parameters among treatments (rows) with different superscripts are
significantly different (lsd; P < 0.05; n = 6).
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MANAGEMENT IMPLICATIONS
Proper management of stream banks is key to maintaining properly functioning
riparian areas. Cattle impact stream banks through two processes: grazing and trampling.
Several studies have shown that loss of cover by grazing can reduce resistance of stream
banks to high flows and increase erosion. Trampling can loosen fragments of soil,
making them more erodible, and hoof action can shear off segments of stream banks,
making them less stable. Our studies show how the following two grazing strategies can
help encourage cattle into uplands and thereby limit stream bank degradation.
Strategy No. 1: Alter Timing of Grazing
Parsons et al. (2003) found that during the cool season of early summer, when
forage quality and quantity were not limiting and ambient air temperatures were
moderate, cattle were evenly distributed across riparian areas. As ambient air temperature
and forage dry matter increased during the hot season of late summer, cattle spent more
time near the stream compared to uplands. We found that grazing during either season
impacted stream banks compared to nongrazed controls. However, grazing during midJune to mid-July, when cattle were attracted to adjacent uplands, limited damage to
stream bank cover and stability compared to grazing later in the year when cattle
congregated in riparian areas. Grazing should not occur so early in the season as to
trample wet soils, but early grazing may have an additional benefit of allowing time for
subsequent regrowth of grazed riparian plants before high flows the following year.
Cattle may behave differently in other geographic areas, and be attracted to uplands at
other times of the year compared to our study in northeastern Oregon. Land managers
must consider timing, as well as frequency and intensity of grazing impacts on individual
streams and even portions of streams to formulate best management practices for meeting
grazing and land management objectives in specific watersheds.
Strategy No. 2: Provide Off-Stream Water and Salt Supplements
These amenities resulted in slightly (though not statistically) less use of stream
banks by cattle compared to nonsupplemented pastures. The difference was enough to
reduce development of uncovered/unstable stream banks threefold.
ACKNOWLEDGEMENTS
This research was funded in part by a grant from the Western Regional SARE Program,
Project AW 95-102. Our appreciation is extended to the Eastern Oregon Agricultural
Research Center for facilities and assistance.
REFERENCES
McInnis, M.L., and J.D. McIver. 2001. Influence of off-stream supplements on stream
banks of riparian pastures. Journal of Range Management 54:648-652.
McInnis, M.L., and J.D. McIver. 2009. Timing of cattle grazing alters impacts on stream
banks in an Oregon mountain watershed. Journal of Soil and Water Conservation. In
Press.
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Parsons, C.T., P.A. Momont, T. DelCurto, M.L. McInnis, and M.L. Porath. 2003. Cattle
distribution patterns and vegetation use in mountain riparian areas. Journal of Range
Management 56:334-341.
Porath, M.L., P.A. Momont, T. DelCurto, N.R. Rimbey, J.A. Tanaka, and M.L. McInnis.
2002. Offstream water and trace mineral salt as management strategies for improved
cattle distribution. Journal of Animal Science 80:346-356.
Roath, L.R., and W.C. Krueger. 1982. Cattle grazing influence on a mountain riparian
zone. Journal of Range Management 35:100-103.
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